As is well known, a vehicle is comprised of one or more differential gears and each of them includes a differential gear set for allowing output shafts to make differential motion, which transmits torque input to a differential case to the pair of output shafts for example.
Sometimes a mechanism for limiting differential motion is contained in the differential case along with the differential gears. For convenience of carrying the mechanism or such therein, a case of a two-piece type, which is dividable into two or more portions, may be used. In the two-piece case, after carrying components into the case, a cover is attached thereto, and, after fastening them together or for the purpose of fixation, a ring gear is fastened to the case. As bolts for the fastening must bear torque transmitted from the ring gear to the case, these bolts must be of a large type and have sufficient strength.
Arts in which welding is used in place of use of the bolts have been proposed. The following documents disclose related arts.    Japanese Patent Application Laid-open No. 2010-91046    US Patent Application Publication 2007/0287570 A1